This invention relates to a heat cycle indicating device.
1. Field of the Invention
More particularly, the invention relates to a heat cycle indicating device for indicating when the device has been subjected to a heat cycle above a predetermined temperature.
2. Description of the Related Art
Some articles are subjected to heat treatment in order to sterilise them. For instance, in the medical field non-disposable equipment is normally autoclaved after each use so that it can be reused. Sometimes the equipment to be autoclaved includes rubber and/or synthetic materials which can be safely autoclaved a limited number of times but when subjected to repeated heat cycling are prone to failure. Normally manufacturers of such equipment will specify the number of times which a particular article can be safely autoclaved before it is disposed of. In practice, however, it is sometimes difficult to accurately keep records of how many times a particular device or piece of equipment has been autoclaved.
It is known to provide in surgical equipment an indicator which indicates the number of times the device has been autoclaved. U.S. Pat. Nos. 5,313,935; 5,359,993and 5,452,335 disclose devices which have an indexing wheel which is acted upon by a bimetallic element. The arrangement is such that on heating and cooling of the device, the bimetallic element rotates the indexing wheel through one step to thereby indicate the number of times the device has been subjected to a heating cycle.
An object of the present invention is to provide an indicating device which is an improvement or simplification of the devices disclosed in the aforementioned patents.
According to the present invention there is provided an indicating device for indicating heat cycling, said device including:
a body including projections;
an indexing element having indexing means the element being mounted for rotation relative to the body;
the arrangement being such that on thermal expansion and contraction of the indexing element, the indexing means thereof engages said projections and cause a step rotation of the indexing element in one sense only relative to the body.
Preferred embodiments of the invention can be constructed in which the only moving part is the indexing element. This constitutes a significant simplification over known techniques and results in a cheaper product which is also more robust and reliable.
In accordance with the invention, the indicating device can be attached to or formed with the body as a surgical instrument or other piece of medical equipment which needs to be sterilised by autoclaving. Each time the equipment is autoclaved, the indexing means operates in association with indicating means so that when the number of safe autoclaving cycles has been reached, the appropriate staff will know that the equipment can no longer be safely used.
In one form of the invention, the indexing means may comprise an expansible ring having projections thereon which are engagable with complementary projections on a base member. During a heating and cooling cycle, the ring expands and is arranged to move relative to the body. Movement of the ring can be viewed relative to the body which may include markings which constitute part of the indicating means.
Preferably further, the ring is bimetallic and rotates about a cylindrical part of the body.
Preferably the indexing occurs after the device has experienced a predetermined temperature increase of 80xc2x0 C. or more.
Preferably further, the body has associated therewith indexing teeth which are engagable with complementary teeth formed on the ring. In the preferred form of the invention, the ring is split and the trailing end of the ring includes a first projection which advances on the indexing teeth when the ring is heated and the leading edge is provided with a second tooth which advances to the next successive indexing tooth on cooling of the ring.